1. Field of the Invention
The invention relates to an image-guided surgery system including a position detection system and a transformation unit.
2. Description of the Related Art
Such an image-guided surgery system is known from U.S. Pat. No. 5,186,174.
During complicated surgery it is often very difficult or even impossible for a surgeon to see directly where in the interior of a patient he/she moves a surgical instrument. Surgery may be aimed at a therapeutic goal, e.g. to remove malignant tissue, or surgery may be aimed at a diagnostic goal e.g. to examine the interior of a patient's anatomy. Surgery includes various methods of entering a patient's body with a surgical instrument. An image guided surgery systems shows the surgeon a position of a surgical instrument in an operating region in the body of a patient during a surgical operation. Before or during the operation images, such as x-ray computed tomography or magnetic resonance images of the patient are formed. During the operation a position detection system measures the position of the surgical instrument relative to the patient and a computer calculates the position in the relevant image which corresponds to the position of the surgical instrument. On a display device the image guided surgery system displays such an e.g. CT or MRI image in which also the actual position of the surgical instrument is indicated. Thus, although the instrument is beyond direct sight to the surgeon, the image guided surgery system enables the surgeon to see where the surgical instrument is inside the patient. The surgeon is thus also able to see how the surgical instrument can be moved in the patient without risk of damaging vital parts.
The position detection system of the known image guided surgery system comprises an articulated arm with potentiometers at its joints for measuring the orientation of the arm. The position detection system includes a data processor for deriving the position in space of the surgical instrument from the signals from the potentiometers.
In the image fiducial markers are imaged which are placed on particular positions on the patient. For example in neurosurgery lead or MR susceptible markers are placed in the area of the patient's head to be operated on. At the start of the operation the fiducial markers are indicated with the surgical instrument or with a separate pointing device and the positions in space of the fiducial markers are measured by the position detection system. For respective markers, their corresponding images of markers in the earlier generated image are also indicated. The data processor calculates the transformation matrix which associates the positions in space of the fiducial markers with the corresponding positions of the images of the markers in the earlier generated image. This transformation matrix is subsequently used to compute a corresponding position in the image for a position in space in the actual operating region.
The article An automatic registration method for frameless stereotaxy, image-guided surgery, and enhanced reality visualization, in IEEE transactions on medical imaging 15(1996)129 by W. E. L. Grimson et al. discloses a transformation which maps a set of measured positions to a surface in segmented MRI data. The method disclosed therein starts from a huge number of hypothetical transformations which map sets of points on the patient to sets of points in the MRI image.